Conventionally, a map data is suitably used for an in-vehicle device. A format of the map data is, for example, a KIWI format, which is disclosed in “Map data format KIWI for a vehicle navigation system,” in DENSO Technical Review, 2001, on Volume 6, Part 1, pages 29-34. With using this format, a road data is shown as a link and a node. A link data of each link for representing a link attribution such as a shape of a link and a street address is stored in the map data.
In a conventional map data, a unique link ID is assigned in each link. The link ID is used for linking a link data corresponding to the link ID with other data. For example, the link ID is used for representing a connection relationship of the link. In a conventional map data, for example, multiple link data are integrated into link sequence data. The link sequence data includes a node data showing a connection relationship of links with using the link ID. The node data relates to a node for connecting links.
Here, the conventional map data includes the link data relating to the link and the node data showing the connection relationship of the links, and therefore, the conventional map data includes information about coordinates of the link data and the node data, which is doubly held in the map data. Thus, it is required to compact the map data, so that storage size of the map data is reduced.